The present invention concerns internal combustion engines with an exhaust gas recirculation device. In particular, the invention concerns the neutralization of acidic condensate in a vehicle furnished with such an internal combustion engine with exhaust gas recirculation.
In order to comply with the exhaust gas regulations for diesel vehicles that are becoming more stringent worldwide, extensive internal and external measures on the engine are required. These measures include, for example, cooled exhaust gas recirculation (EGR) that enables a significant reduction of the nitrogen oxide emissions. The realization of the EGR can be done with a conventional high-pressure EGR circuit or with a low-pressure EGR circuit. In the latter case, a portion of the exhaust gas is removed downstream of the turbine and the particle filter, recirculated and mixed with fresh air upstream of the compressor.
Within the motor water is produced by fuel combustion that then leaves via the exhaust system in the form of water vapor. In this connection, for example, in case of a truck, several cubic meters of water per 100,000 km are produced. By using exhaust gas recirculation a reduction of the NOx values is achieved. Currently, mainly the high-pressure EGR system variety is employed that however has several disadvantages in comparison to the low-pressure EGR system. When using low-pressure EGR systems, as mentioned before, a portion of the exhaust gas downstream of the diesel particulate filter is supplied to an exhaust gas cooler which then cools the already expanded exhaust gas. By means of the EGR cooler, a cooling to below the dew point (80 to 140EC) of the water-soluble media (H2SO4, H2SO3, HNO3, HCl and H3PO4) contained in the exhaust gas is achieved which leads to the formation of acidic condensates. Because of the acidic condensate (pH approximately 1.5-5) all components downstream including the EGR cooler are subject to strong corrosion which can lead to their destruction when they are not made from appropriate high-quality materials or coated in an expensive way.
Accordingly, it is necessary to neutralize the produced acidic condensate in order to increase the service life of the components.
U.S. Pat. No. 5,857,324 discloses a device and a method for removal of gases and particulate material from automobile exhaust gas. The device comprises a heat exchanger connected to the automobile exhaust gas system for cooling exhaust gas and for condensing at least a portion of the exhaust gases to a liquid condensate. The condensate and at least one part of the particulate material are separated from the gases that are not condensed and the condensate is returned into a liquid-filled tank. In a first chemical reactor the condensate is treated wherein the acids present in the liquid are neutralized, for example, by means of an alkali metal hydroxide.
U.S. 2004/0050373 A1 discloses a device and a method for improving the service life of lubricant oil in a diesel engine with an EGR system. For this purpose, a chemical filter is positioned either in the EGR flow or in the vicinity of the intake socket; the filter filters out the acidic components from the EGR stream before they can enter the intake socket. In this connection, metal carbonates, metal oxides, metal hydroxides, active carbon, ion exchange materials and other natural adsorbent materials such as limestone are employed as adsorbent materials.
A disadvantage of these solutions is that upon neutralization solid materials, for example, calcium sulfate and the like, are produced which must be disposed of separately. Moreover, their efficiency is locally limited, i.e., the reaction takes place, for example, only within the limestone fill. When the neutralization then is not complete, there is still acidic medium present. Depending on the expected condensate quantity, large quantities of resin (i.e. ion exchanger) are required. Moreover, for chemical neutralization, particularly with respect to weak acids, significant time expenditure is required in order to obtain a satisfactory neutralization (pH 6-7).
Since not all salts of the existing acids will deposit as a solid material, the water-soluble salts in the system can migrate further and can deposit on heat-exposed components in the internal combustion engine (valves, movable parts, etc.) and thus form a corresponding coating (salt layer). Thus, even though a neutralization would be achieved, there remains the disadvantage of possible deposits on hot surfaces where the water will evaporate and the salt will remain as a deposit.
It is therefore an object of the present invention to provide a device and a method for neutralization of acidic condensate in internal combustion engines with EGR system for the purpose of avoiding the disadvantages of the prior art.
It is another object of the present invention to provide such a device and corresponding method whose function is fast, reliable and requires only minimal space.